1. Field of the Invention
The present invention is in the field of tool path creation for computer controlled cutting operations. Particularly the invention relates to creating tool paths which minimize the appearance of undesirable tool marks and articles of manufacture created using the novel tool paths.
2. Summary of the Prior Art
Conventional CNC (computer numeric control) manufacturing refers to the use of a type of computerized industrial tool in which the motion of a cutting tool is dictated by computerized commands. The type of CNC used for carving is generally known as a CNC router and consists of a table with a moving gantry on which a moving router or spindle is mounted. The spindle or router carves a target surface with differently sized and shaped router bits.
One use for CNC routers is producing a textured panel for use on a wall inside a building. Several companies now produce carved, textured panels for ornamental purposes with CNC machinery. These textured panels are used to cover entire walls or parts of walls, the fronts of reception desks, as cabinet and entry doors and for other decorative purposes. The material used for them is often MDF (medium density fiberboard) but it can also be natural wood, plastics or other materials.
Textured panels are mostly produced by passing a large round-end (also known as a ball-nose) router bit over the surface in specific paths to carve the textures as quickly as possible. In some cases straight or v-shaped bits are used. Currently available textured panel designs almost entirely consist of abstract texture but also include some line patterns which are representational of flowers or scrollwork. These representational patterns are created in the manner of line drawings with the router bits carving simple lines into the surface at a uniform height.
Another category of relief carving exists besides the carving of textures, bas relief. Bas relief sculpture is found on classical carved furniture, older building facades or the surfaces of coins where faces of American Presidents and other notables or buildings or birds and animals are sculpturally represented. This type of carving is differentiated from that used to create contemporary textured panels whose designs consist of a myriad of completely abstract textures or textures suggesting patterns like the surface of flowing water or a brick wall. Textured panels as they exist today do not normally represent actual objects such as leaves or fruit or the forms of classical ornament but if they do, these textures take the form of simple line drawings milled at constant depth. The primary reason is that the CNC production of representations of actual objects with conventional techniques results in undesirable tool marks and requires a very large amount of machine time in order to prevent the need for secondary processing.
CNC machinery is fully capable of producing traditional complex bas-relief carving with fine detail, however the process requires that smaller router bits are passed many times (often over 100 passes per linear inch) over each section of the carving to achieve acceptable results. Carvings such as these are offered today by many makers of carved ornament such as Enkeboll Designs. It would be considered desirable to offer more defined carved motifs, yet because of the high levels of production time required complex sculpted reliefs such as these or any other type of representative reliefs are not offered by the makers of textured panels.
Additionally in carving of representative reliefs where small bits are used and the machine may make 100 passes per inch the router bit leaves slightly visible marks in the form of grooves and peaks on the underlying relief. These grooves and peaks are known as tool marks. The grooves and peaks in conventional CNC operation are perfectly parallel to each other. If small enough the marks are accepted and generally meet industry and consumer standards but they are often sanded away since they impart a machine-made look to the carvings. The tool marks are considered undesirable and would generally be avoided if a technique were available to carve finely detailed or representative work without them.
Additionally, in general, a larger diameter bit can cut a relief with less passes, however a larger diameter tool will leave larger tool marks if each pass is stepped over a large distance, as results when cutting with less passes. Thus, even though a larger tool can perform a cutting operation quicker, because of the undesirable effects of larger tool marks which result with currently used tool path creation methods, CNC carving remains a slow process.
One way to decrease required carving time it to increase the material removed with each pass of a cutter being operated along a given contour of a tool path. A basic concept of carving into materials with CNC machinery is to never put so much load on your cutting tool that it breaks. Conventionally the rule has been to never carve down deeper than the diameter of the bit on one pass. So when carving at a maximum depth of 1″ with a ¼″ diameter cutting tool a tool path is constructed which directs the cutting tool to cut away ¼″ of material from all deeper areas, then another pass of ¼″ and then another. Only then may the final pattern of tool paths be run which will carve the final surface without ever making a cut deeper than ¼″. This process may involve several different sized and shaped bits and takes a large amount of machine time but it is the conventional approach to CNC carving. The staggered depth of cut described above increases the time required to carve a given relief.
There is a need in the art for a method of tool path creation for CNC machines which enables an operator to remove material from a target surface quicker and with reduced appearance of tool marks oriented so that they create a regular machine made appearance.